Surface acoustic wave bandgaps in a two-dimensional composite piezoelectric phononic crystal

A two-dimensional composite piezoelectric phononic crystal was proposed, which is composed of a thin epoxy at the bottom and a nickel pillar at the top and deposited on the lithium niobate substrate. The dispersion relation of the structure was calculated by a finite element method, the bandgap characteristics of the composite piezoelectric phononic crystal were also carefully analyzed. The results show that the effective elastic modulus of the scatterer is reduced by introducing epoxy, so that the complete band gap of the surface acoustic waves (SAWs) is reduced and multiple SAW directional band gaps are opened. The transmission spectra were calculated to verify the existence of the band gap, and its transmission characteristics were discussed. The mechanism of band gap formation was analyzed by using the displacement fields of different eigenmodes at the edge X of Brillouin zone. Furthermore, the effect of the geometric parameters of the pillar on the SAW complete band gap and XM direction SAW band gap characteristics were also studied. It is found that, as the thickness of epoxy increases, multi-band gaps in the XM direction will merge to form a wide band gap of 158 MHz. The research content provides a reference for designing of electroacoustic equipment based on phononic crystal. © 2021, Editorial Office of Journal of Vibration and Shock. All right reserved.